This invention relates to voltage regulators, more particularly to a voltage regulator having an output stage isolated electrically from the regulator stage, and specifically to a voltage regulator for use with series-connected batteries connected to a direct current alternator or generator which provides the same potential as the higher voltage battery of the series and wherein the voltage regulator regulates on the voltage of the lower voltage battery of the series.
Voltage regulators of the type heretofore employed in vehicles have been characterized by certain disadvantages and limitations. Their ground-connecting lead is susceptible of breaking, whereupon the regulator goes out of control. Their output is biased "on", and therefore when the sensing voltage lead is broken, as occurs occasionally, the regulator goes out of control. Further, being biased "on" the regulator operates at elevated temperatures which require more power for control. Their output is not isolated from the regulator stage, whereupon switching of the fields produces undesirable transient signals which, unless filtered out, result in erratic operation of the regulator.
Dual voltage electrical systems are finding increased utility on vehicles, boats and other industrial equipment, because of the availability of diverse sophisticated battery powered devices of diverse voltage requirements.
As an illustration, some industrial equipment is provided with a 24 volt direct current electrical system and yet it requires some 12 volt direct current load, such as a radio or a transceiver.
Such dual voltage systems may be provided conveniently and economically by an arrangement of series-connected 12 volt batteries. Because of the unbalanced battery load, separate regulated charge control is required for each battery. Applicant's earlier U.S. Pat. No. 4,041,363 provides such dual voltage control and maintains battery balance. However, it is a requirement that the alternator must be of the same voltage as the battery of the lower voltage output, since the alternator regulator must regulate the lower output voltage battery of the series while the dual voltage control regulates the higher voltage output battery of the series.
On the other hand, it is becoming an ever-increasing problem that certain types of industrial equipment are provided with a 24 volt electrical system, including a 24 volt alternator. Thus, in providing an additional 12 volt source, there has been no alternative heretofore to the extremely costly replacement of the 24 volt alternator with a 12 volt alternator. Indeed, certain systems have been impossible of such modification because of requirements of special housings and other components.